Add diagnostics for semicolon at the end of while body

This change introduce diagnostics when there is a semicolon at
the end of the while loop body:
```cpp
  i := 0;
  while i* < container.size() next i++ {
    std::cout << container[i] << std::endl;
  };
```
generates:
```
error: while loop body shall not end with a semicolon (at ';')
```

Author: filipsajdak

source/parse.h

@@ -4208,6 +4208,10 @@ class parser
             if (!handle_logical_expression  ()) { return {}; }
             if (!handle_optional_next_clause()) { return {}; }
             if (!handle_compound_statement  ()) { return {}; }
+            if (!done() && curr().type() == lexeme::Semicolon) {
+                error("a loop body may not be followed by a semicolon (empty statements are not allowed)");
+                return {};
+            }
             return n;
         }